METHOD AND APPARATUS FOR DEWATERING OF A FIBRE SUSPENSION

Abstract: In a method for the conversion of a fibre suspension, and particularly for increasing the output of a dewatering apparatus especially for recycled fibre pulp, the reject from the dewatering apparatus is treated in a fractionator, where fractioning takes place in liquid, and fractions from the fractionator are selectively introduced into the accept flow from the dewatering apparatus. In an apparatus for practising the method, a fractionator (10) of the kind where fractioning takes place in liquid is connected to the reject outlet (8) of a dewatering apparatus (1), and the fraction outlets (18, 19, 20) of the fractionator lead to the accept outlet (6) of the dewatering apparatus (1).

Description: Method and apparatus for dewatering of a fibre suspens ion. The present invention concers a method and an apparatus for the conversion of a fibre suspension and particularly for increasing the output of a dewatering apparatus especially for recycled fibre pulp. With the reject from dewatering apparatuses, such as so-called thin film washers, screw presses, disk filters etc., is brought along not only fine particles, such as so-called fines and fillers, but also a relatively large share of valuable fibres (long fibre fraction) . It is an economical as well as an environmental desire to be able to recover not only the latter, but also the fine particles to re-introduce them into the process. Hitherto, this has taken place in flotation apparatuses, filters etc. Now, according to the present invention, an alternative method is proposed, wherein the reject from a dewatering apparatus is treated in a fractionator, where fractioning takes place in liquid, and wherein the fractions from the fractionator are selectively introduced into the accept- flow from the dewatering apparatus. According to the present invention, this can be accomplished in that a fractionator, wherein fractioning takes place in liquid, is connected to a reject outlet of a dewatering apparatus, and that fraction outlets of the fractionator lead to an accept outlet of the dewatering apparatus. According to the present invention it is now possible to control the quality of the accept of a dewatering apparatus by fractioning the reject and supply fractions of the reject to the accept. The invention will be further elucidated hereinafter, reference being made to an exemplifying embodiment illustrated in the attached drawing, wherein the sole figure shows a schematic view of an apparatus according to the present invention. In the drawing, 1 designates any dewatering apparatus, herein shown as a so-called thin film washer of the kind described in Swedish Patent Application No. 9303192-0, filed September 30, 1994 and entitled "Apparatus for washing of fibre suspension" . Diluted recycled fibre pulp (about 1%) is introduced therein through an inlet 2. Water is pressed out of the pulp through a perforated drum 3, and the dewatered pulp (about 8%) is removed from the drum by means of a roller 4 and a scraper 5 and is discharged through an outlet conduit 6. The pressed out water, which contains long fibres, fines as well as fillers, is discharged from a container 7 through an outlet 8. To the outlet 8 is connected the inlet 9 of a fractionator 10 fractioning in liquid, i.e., an apparatus utilizing the fluid flow phenomenon resulting in that larger particles in a flowing liquid are displaced forwardly in the direction of flow, whereas smaller particles are displaced relatively seen backwards in the direction of flow. Thus, there is formed in a flowing plug of, for instance, a suspension, a fractioning in a diminishing particle size from the front and backwards in the plug. The fractionator shown is of the kind described in Swedish Patent Application No. 9303193-8, filed September 30, 1994 and entitled "Fractionator". Such a fractionator is provided with a rotatable cylindrical drum 11, within which are provided a plurality of cylinders 12, 13, 14, 15 and 16 concentric to the drum. Every second such cylinder is tightly connected in its one end to one end wall of the drum, while flow can take place between the other end of the cylinder and the opposite end wall of the drum. Suspension from the outlet 8 of the dewatering apparatus introduced into the centre of the drum through the inlet 9, thus, flows forwards and backwards between the end walls of the drum and simultaneously outwards towards the drum mantle 17, where the fractionator is provided with outlets for several fractions, in the example shown one outlet 18 for short fibres, one outlet 19 for fines and one outlet 20 for fillers, such as ash and clay. The outlets 18, 19 and 20 are connected to outlet conduits 21, 22, 23, respectively, which in turn and in a non-shown manner are connected to the outlet conduit 6 of the dewatering apparatus. Suitably, the outlet conduits lead to non-shown tanks for the different fractions, wherefrom the fractions may be selectively introduced into the outlet conduit 6 of the dewatering apparatus in order to re-introduce into the concentrated pulp flow present in the outlet conduit 6 selected amounts of selected fractions from the fractionator. The fraction or fractions to be introduced into the outlet conduit 6, as well as the amounts thereof, are determined by sensing the quality of the pulp at the inlet 2 of the dewatering apparatus and/or its outlet 6.

Claims: CLAIMS 1. Method for the conversion of a fibre suspension, and particularly for increasing the output of a dewatering apparatus especially for recycled fibre pulp, c h a r a c ¬ t e r i z e d i n that reject from the dewatering apparatus is treated in a fractionator, where fractioning takes place in liquid, and that fractions from the fractionator are selectively introduced into an accept flow from the dewatering apparatus. 2. Method according to claim 1, c h a r a c t e r i z e d i n that the fractions from the fractionator are introduced into the accept flow from the dewatering apparatus in dependence on the established quality thereof. 3. Apparatus for the conversion of a fibre suspension, and particularly for increasing the output of a dewatering apparatus especially for recycled fibre pulp, c h a r a c - t e r i z e d i n that to a reject outlet (8) of a dewatering apparatus (1) is connected a fractionator (10) , wherein fractioning takes place in liquid, and that fraction outlets (18, 19, 20) of the fractionator lead to an accept outlet (6) of the dewatering apparatus (1) . 4. Apparatus according to claim 3, c h a r a c t e r i z e d b y means for sensing the suspension quality at an inlet (2) and/or the outlet (6) of the dewatering apparatus. 5. Apparatus according to claim 4, c h a r a c t e r i z e d b y means between the fraction outlets (18, 19, 20) of the fractionator and the accept outlet (6) of the dewatering apparatus for controlling the supply of fractions to the accept outlet in dependence on the suspension quality sensed.

Inventors: STRID KENT, STRID, KENT
Applicants: KVAERNER PULP EQUIP AS, STRID KENT, KVAERNER PULP EQUIPMENT A.S, STRID, KENT
Application year: 1994
Main classification: D21C9
IPC codes: B01D24, B01D33, D21C9, D21D1, D21D5, D21F1